Former Twitter CEO Dick Costolo took to Twitter (where else?) on Tuesday to announce his latest undertaking: a platform for personal fitness that will "make the road to personal transformation fun and social." Sharing screenshots of his Notes app, Costolo explained that the new company would "go beyond measurement to motivate," supplementing the work of wellness professionals like cofounder Bryan Oki.

"The fitness industry is transitioning to a world of specialized studios and programs with a multitude of connected devices and software trackers," Costolo wrote. "We’ve developed a system that works within this evolving landscape, and we believe we can scale this system with technology and deliver it to a massive audience." It's not yet clear how this fitness platform will stand apart from existing fare, but Costolo assures skeptics that its prototypes already show promise.

Costolo will also join venture capital firm Index Ventures, where he will invest in startups and advise budding entrepreneurs.

When Twitter’s user growth problems brought scrutiny from Wall Street and others, Mr. Costolo found solace in his fitness regimen, which consisted of everything from CrossFit workouts to bike sprints to weight training.